Aqueous solutions often contain one or more contaminants. Such aqueous solutions include, but are not limited to, hydraulic fracturing fluid, hydraulic fracturing backflow water, high-salinity solutions, groundwater, seawater, wastewater, drinking water, aquaculture (e.g., aquarium water and aquaculture water), ballast water, and textile industry dye wastewater. Further information on example aqueous solutions follows.
Hydraulic fracturing fluid includes any fluid or solution utilized to stimulate or produce gas or petroleum, or any such fluid or solution after it is used for that purpose.
Groundwater includes water that occurs below the surface of the Earth, where it occupies spaces in soils or geologic strata. Groundwater may include water that supplies aquifers, wells and springs.
Wastewater may be any water that has been adversely affected in quality by effects, processes, and/or materials derived from human or non-human activities. For example, wastewater may be water used for washing, flushing, or in a manufacturing process, that contains waste products. Wastewater may further be sewage that is contaminated by feces, urine, bodily fluids and/or other domestic, municipal or industrial liquid waste products that is disposed of (e.g., via a pipe, sewer, or similar structure or infrastructure or via a cesspool emptier). Wastewater may originate from blackwater, cesspit leakage, septic tanks, sewage treatment, washing water (also referred to as “graywater”), rainfall, groundwater infiltrated into sewage, surplus manufactured liquids, road drainage, industrial site drainage, and storm drains, for example.
Drinking water includes water intended for supply, for example, to households, commerce and/or industry. Drinking water may include water drawn directly from a tap or faucet. Drinking water may further include sources of drinking water supplies such as, for example, surface water and groundwater.
Aquarium water includes, for example, freshwater, seawater, and saltwater used in water-filled enclosures in which fish or other aquatic plants and animals are kept or intended to be kept. Aquarium water may originate from aquariums of any size such as small home aquariums up to large aquariums (e.g., aquariums holding thousands to hundreds of thousands of gallons of water).
Aquaculture water is water used in the cultivation of aquatic organisms. Aquaculture water includes, for example, freshwater, seawater, and saltwater used in the cultivation of aquatic organisms.
Ballast water includes water, such as freshwater and seawater, held in tanks and cargo holds of ships to increase the stability and maneuverability during transit. Ballast water may also contain exotic species, alien species, invasive species, and/or nonindiginous species of organisms and plants, as well as sediments and contaminants.
A contaminant may be, for example, an organism, an organic chemical, an inorganic chemical, and/or combinations thereof. More specifically, “contaminant” may refer to any compound that is not naturally found in an aqueous solution. Contaminants may also include microorganisms that may be naturally found in an aqueous solution and may be considered safe at certain levels, but may present problems (e.g., disease and/or other health problems) at different levels. In other cases (e.g., in the case of ballast water), contaminants also include microorganisms that may be naturally found in the ballast water at its point of origin, but may be considered non-native or exotic species. Moreover, governmental agencies such as the United States Environmental Protection Agency, have established standards for contaminants in water.
A contaminant may include a material commonly found in hydraulic fracturing fluid before or after use. For example, the contaminant may be one or more of the following or combinations thereof: diluted acid (e.g., hydrochloric acid), a friction reducer (e.g., polyacrylamide), an antimicrobial agent (e.g., glutaraldehyde, ethanol, and/or methanol), scale inhibitor (e.g., ethylene glycol, alcohol, and sodium hydroxide), sodium and calcium salts, barium, oil, strontium, iron, heavy metals, soap, bacteria, etc. A contaminant may include a polymer to thicken or increase viscosity to improve recovery of oil. A contaminant may also include guar or guar gum, which is commonly used as a thickening agent in many applications in oil recovery, the energy field, and the food industry.
A contaminant may be an organism or a microorganism. The microorganism may be for example, a prokaryote, a eukaryote, and/or a virus. The prokaryote may be, for example, pathogenic prokaryotes and fecal coliform bacteria. Example prokaryotes may be Escherichia, Brucella, Legionella, sulfate reducing bacteria, acid producing bacteria, Cholera bacteria, and combinations thereof.
Example eukaryotes may be a protist, a fungus, or an algae. Example protists (protozoans) may be Giardia, Cryptosporidium, and combinations thereof. A eukaryote may also be a pathogenic eukaryote. Also contemplated within the disclosure are cysts of cyst-forming eukaryotes such as, for example, Giardia. 
A eukaryote may also include one or more disease vectors. A “disease vector” refers any agent (person, animal or microorganism) that carries and transmits an infectious pathogen into another living organism. Examples include, but are not limited to, an insect, nematode, or other organism that transmits an infectious agent. The life cycle of some invertebrates such as, for example, insects, includes time spent in water. Female mosquitoes, for example, lay their eggs in water. Other invertebrates such as, for example, nematodes, may deposit eggs in aqueous solutions. Cysts of invertebrates may also contaminate aqueous environments. Treatment of aqueous solutions in which a vector (e.g., disease vector) may reside may thus serve as a control mechanism for both the disease vector and the infectious agent.
A contaminant may be a virus. Example viruses may include a waterborne virus such as, for example, enteric viruses, hepatitis A virus, hepatitis E virus, rotavirus, and MS2 coliphage, adenovirus, and norovirus.
A contaminant may include an organic chemical. The organic chemical may be any carbon-containing substance according to its ordinary meaning. The organic chemical may be, for example, chemical compounds, pharmaceuticals, over-the-counter drugs, dyes, agricultural pollutants, industrial pollutants, proteins, endocrine disruptors, fuel oxygenates, and/or personal care products. Examples of organic chemicals may include acetone, acid blue 9, acid yellow 23, acrylamide, alachlor, atrazine, benzene, benzo(a)pyrene, bromodichloromethane, carbofuran, carbon tetrachloride, chlorobenzene, chlorodane, chloroform, chloromethane, 2,4-dichlorophenoxyacetic acid, dalapon, 1,2-dibromo-3-chloropropane, o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, dichlormethane, 1,2-dichloropropane, di(2-ethylhexyl)adipate, di(2-ethylhexyl)phthalate, dinoseb, dioxin (2,3,7,8-TCDD), diquat, endothall, endrin, epichlorohydrin, ethylbenzene, ethylene dibromide, glyphosate, a haloacetic acid, heptachlor, heptachlor epoxide, hexachlorobenzene, hexachlorocyclopentadiene, lindane, methyl-tertiary-butyl ether, methyoxychlor, napthoxamyl (vydate), naphthalene, pentachlorophenol, phenol, picloram, isopropylbenzene, N-butylbenzene, N-propylbenzene, Sec-butylbenzene, polychlorinated biphenyls (PCBs), simazine, sodium phenoxyacetic acid, styrene, tetrachloroethylene, toluene, toxaphene, 2,4,5-TP (silvex), 1,2,4-trichlorobenzene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, a trihalomethane, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, vinyl chloride, o-xylene, m-xylene, p-xylene, an endocrine disruptor, a G-series nerve agent, a V-series nerve agent, bisphenol-A, bovine serum albumin, carbamazepine, cortisol, estradiol-17β, gasoline, gelbstoff, triclosan, ricin, a polybrominated diphenyl ether, a polychlorinated diphenyl ether, and a polychlorinated biphenyl. Methyl tert-butyl ether (also known as, methyl tertiary-butyl ether) is a particularly applicable organic chemical contaminant.
A contaminant may include an inorganic chemical. More specifically, the contaminant may be a nitrogen-containing inorganic chemical such as, for example, ammonia (NH3) or ammonium (NH4). Contaminants may include non-nitrogen-containing inorganic chemicals such as, for example, aluminum, antimony, arsenic, asbestos, barium, beryllium, bromate, cadmium, chloramine, chlorine, chlorine dioxide, chlorite, chromium, copper, cyanide, fluoride, iron, lead, manganese, mercury, nickel, nitrate, nitrite, selenium, silver, sodium, sulfate, thallium, and/or zinc.
A contaminant may include a radionuclide. Radioactive contamination may be the result of a spill or accident during the production or use of radionuclides (radioisotopes). Example radionuclides include, but are not limited to, an alpha photon emitter, a beta photon emitter, radium 226, radium 228, and uranium.
Various methods exist for handling contaminants and contaminated aqueous solutions. Generally, for example, contaminants may be contained to prevent them from migrating from their source, removed, and immobilized or detoxified.
Another method for handling contaminants and contaminated aqueous solutions is to treat the aqueous solution at its point-of-use. Point-of-use water treatment refers to a variety of different water treatment methods (physical, chemical and biological) for improving water quality for an intended use such as, for example, drinking, bathing, washing, irrigation, etc., at the point of consumption instead of at a centralized location. Point-of-use treatment may include water treatment at a more decentralized level such as a small community or at a household. A drastic alternative is to abandon use of the contaminated aqueous solutions and use an alternative source.
Other methods for handling contaminants and contaminated aqueous solutions are used for removing gasoline and fuel contaminants, and particularly the gasoline additive, MTBE. These methods include, for example, phytoremediation, soil vapor extraction, multiphase extraction, air sparging, membranes (reverse osmosis), and other technologies. In addition to high cost, some of these alternative remediation technologies result in the formation of other contaminants at concentrations higher than their recommended limits. For example, most oxidation methods of MTBE result in the formation of bromate ions higher than its recommended limit of 10 μg/L in drinking water (Liang et al., “Oxidation of MTBE by ozone and peroxone processes,” J. Am. Water Works Assoc. 91:104 (1999)).
A number of technologies have proven useful in reducing MTBE contamination, including photocatalytic degradation with UV light and titanium dioxide (Barreto et al., “Photocatalytic degradation of methyl tert-butyl ether in TiO2 slurries: a proposed reaction scheme,” Water Res. 29:1243-1248 (1995); Cater et al., “UV/H2O2 treatment of MTBE in contaminated water,” Environ. Sci Technol. 34:659 (2000)), oxidation with UV and hydrogen peroxide (Chang and Young, “Kinetics of MTBE degradation and by-product formation during UV/hydrogen peroxide water treatment,” Water Res. 34:2223 (2000); Stefan et al., “Degradation pathways during the treatment of MTBE by the UV/H2O2 process,” Environ. Sci. Technol. 34:650 (2000)), oxidation by ozone and peroxone (Liang et al., “Oxidation of MTBE by ozone and peroxone processes,” J. Am. Water Works Assoc. 91:104 (1999)) and in situ and ex situ bioremediation (Bradley et al., “Aerobic mineralization of MTBE and tert-Butyl alcohol by stream bed sediment microorganisms,” Environ. Sci. Technol. 33:1877-1879 (1999)).
Use of titanium dioxide (titania, TiO2) as a photocatalyst has been shown to degrade a wide range of organic pollutants in water, including halogenated and aromatic hydrocarbons, nitrogen-containing heterocyclic compounds, hydrogen sulfide, surfactants, herbicides, and metal complexes (Matthews, “Photo-oxidation of organic material in aqueous suspensions of titanium dioxide,” Water Res. 220:569 (1986); Matthews, “Kinetic of photocatalytic oxidation of organic solutions over titanium-dioxide,” J. Catal. 113:549 (1987); Ollis et al., “Destruction of water contaminants,” Environ. Sci. Technol. 25:1522 (1991)).
Irradiation of a semiconductor photocatalyst, such as titanium dioxide (TiO2), zinc oxide, or cadmium sulfide, with light energy equal to or greater than the band gap energy (Ebg) causes electrons to shift from the valence band to the conduction band. If the ambient and surface conditions are correct, the excited electron and hole pair can participate in oxidation-reduction reactions. The oxygen acts as an electron acceptor and forms hydrogen peroxide. The electron donors (i.e., contaminants) are oxidized either directly by valence band holes or indirectly by hydroxyl radicals (Hoffman et al., “Photocatalytic production of H2O2 and organic peroxide on quantum-sized semi-conductor colloids,” Environ. Sci. Technol. 28:776 (1994)). Additionally, ethers can be degraded oxidatively using a photocatalyst such as TiO2 (Lichtin et al., “Photopromoted titanium oxide-catalyzed oxidative decomposition of organic pollutants in water and in the vapor phase,” Water Pollut. Res. J. Can. 27:203 (1992)). A reaction scheme for photocatalytically destroying MTBE using UV and TiO2 has been proposed, but photodegradation took place only in the presence of catalyst, oxygen, and near UV irradiation and MTBE was converted to several intermediates (tertiary-butyl formate, tertiary-butyl alcohol, acetone, and alpha-hydroperoxy MTBE) before complete mineralization (Barreto et al. “Photocatalytic degradation of methyl tert-butyl ether in TiO2 slurries: a proposed reaction scheme,” Water Res. 29:1243-1248 (1995)).
A more commonly used method of treating aqueous solutions for disinfection of microorganisms is chemically treating the solution with chlorine. Disinfection with chlorine, however, has several disadvantages. For example, chlorine content must be regularly monitored, formation of undesirable carcinogenic by-products may occur, chlorine has an unpleasant odor and taste, and chlorine requires the storage of water in a holding tank for a specific time period.
Aqueous solutions used for hydraulically fracturing gas wells (e.g., fracturing or frac fluids) or otherwise stimulating petroleum, oil and/or gas production also require treatment. Such solutions or frac fluids typically include one or more components or contaminants including, by way of example and without limitation, water, sand, diluted acid (e.g., hydrochloric acid), one or more polymers or friction reducers (e.g., polyacrylamide), one or more antimicrobial agents (e.g., glutaraldehyde, ethanol, and/or methanol), one or more scale inhibitors (e.g., ethylene glycol, alcohol, and sodium hydroxide), and one or more thickening agents (e.g., guar). In addition, a significant percentage of such solutions and fluids return toward the Earth surface as flowback, and later as produced water, after they have been injected into a hydrofrac zone underground. As they return toward the Earth surface, the solutions and fluids also pick up other contaminants from the earth such as salt (e.g., sodium and calcium salts). Such fluids may also include barium, oil, strontium, iron, heavy metals, soap, high concentrations of bacteria including acid producing and sulfate reducing bacteria, etc.
Aqueous solutions used for hydraulically fracturing gas wells or otherwise stimulating oil and gas production are difficult and expensive to treat for many reasons including, without limitation, the salinity of the solutions. For that reason, such fluids are often ultimately disposed of underground, offsite, or into natural water bodies. In some cases, certain states and countries will not allow fracking due to remediation concerns.
Accordingly, there is a need in the art for alternative approaches for treating aqueous solutions to remove and/or reduce amounts of contaminants. Specifically, it would be advantageous to have apparatus and/or methods for treating various aqueous solutions including hydraulic fracturing fluid, hydraulic fracturing backflow water, high-salinity water, groundwater, seawater, wastewater, drinking water, aquarium water, and aquaculture water, and/or for preparation of ultrapure water for laboratory use and remediation of textile industry dye wastewater, among others, that help remove or eliminate contaminants without the addition of chemical constituents, the production of potentially hazardous by-products, or the need for long-term storage.